Motorists are not able to accurately judge the distance another vehicle will need to stop safely. As a result, those driving smaller vehicles, such as cars and sport utility vehicles, pass larger trucks and then merge back into the lane of travel in front of the vehicle they just passed. While they may (or may not) leave themselves enough distance to stop before hitting the car in front of them, they do not leave enough distance for the truck behind to stop without hitting them, creating a dangerous situation. For example, see the following chart comparing the stopping distances for cars and trucks.
Stopping Distances for Cars Versus TrucksReaction/BrakingReaction/BrakingStoppingStoppingDistanceDistanceDistanceDistanceSpeedCarsTrucksCarsTrucks40 mph44′/80′ 44′/125′124′169′55 mph60′/165′60′/275′225′335′65 mph71′/245′71′/454′316′525′*Above estimates are for 80,000 lb., loaded tractor-trailers and mid-size passenger cars traveling on a dry, level road.Source: National Safety Council's Defensive Driving Course for Professional Truck Drivers.
While some systems exist for prototype “self-driving” cars to determine their own stopping distances, or for the driver of a vehicle to determine the stopping distance of the driver's own vehicle in order to maintain a safe following distance, no system exists that gives passing vehicles the information they need regarding the stopping distance of the vehicle they are passing.
Needs exist for a system that indicates the stopping distance of a vehicle to other vehicles that are passing it.